This application claims priority to Korean Patent Application No. 2003-0079904, filed on Nov. 12, 2003, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference.
1. Field of the Invention
The present invention relates generally to terrestrial digital video broadcasting (DVB-T) receivers, and more particularly, to a mode detector and method for determining a guard interval (GI) mode and a FFT mode of an I/Q (in-phase and quadrature) stream within a DVB-T receiver.
2. Description of the Related Art
In terrestrial digital video broadcasting (DVB-T), a high number of carrier signals are used with Orthogonal Frequency Division Multiplexing (OFDM) as defined by the IEEE 802.11 standard protocol, and as known to one of ordinary skill in the art of DVB-T technology. A data frame of a DVB-T transmission signal is comprised of 68 OFDM symbols with each symbol including 1705 active carriers in a 2K mode or 6817 active carriers in an 8K mode. The DVB-T standard defines the 2K mode and the 8K mode. More specifically, the 2K mode and the 8K mode, each commonly referred to as “a FFT mode”, also dictate the size of an FFT active window processed by a DVB-T receiver.
Because terrestrial digital video broadcasting is over uncertain transmission paths, a guard interval is inserted into each OFDM symbol, as illustrated in FIG. 7. FIG. 7 illustrates an example OFDM symbol 702 in a series of OFDM symbols (with a previous OFDM symbol 704 and a next OFDM symbol 706 shown in FIG. 7). The example OFDM symbol 702 is comprised of an active symbol 708 and a guard interval 710. Typically, the guard interval 710 is formed by copying an end portion 712 of the OFDM symbol 702 to the guard interval portion 710.
Each OFDM symbol includes such a respective guard interval formed by copying a respective end portion of the OFDM symbol. Such guard intervals are used to correct for degradation to signal quality from reflections during transmission of the DVB-T transmission signal. For example, when tall objects such as buildings are in the transmission path, the DVB-T transmission signal may be reflected from such buildings such that the DVB-T transmission signal is received twice at a DVB-T receiver. The guard interval of each OFDM symbol is used for correcting for signal interference from such reflection of the DVB-T transmission signal.
However, the guard interval of each OFDM symbol is desired to be removed before the received DVB-T signal is further processed. Referring to FIG. 7, the length of the guard interval 710 is formed to be a fraction the length of the OFDM symbol 702. In particular, the length of the guard interval 710 is formed to be one of 1/32, 1/16, ⅛, or ¼ of the length of the OFDM symbol 702. Such fractions define the GI (guard interval) mode of the DVB-T transmission signal.
When the DVB-T transmission signal is received as a bit stream at the DVB-T receiver, a FFT mode and a GI mode for the received bit stream is determined for removal of the guard interval of each OFDM symbol. Thereafter, an FFT (Fast Fourier Transform) is performed on the resultant bit stream using an active window size with 2K (2048) or 8K (8192) points according to the FFT mode.
A conventional DVB-T receiver is typically capable of performing an FFT with respect to a constant FFT mode and a GI mode. Therefore, the conventional DVB-T cannot perform an FFT on an input bit stream from a channel operating with changing operating modes. In this regard, Korean Patent No. KR10-0327373 discloses a conventional receiver capable of detecting a changing operating mode. Nevertheless, it is still desired to increase the precision of determining the FFT and GI modes of the bit stream with minimized cost of the DVB-T receiver.